There has been an increasing interest in the ability to measure position of the fingers and hand in such areas as virtual reality, telerobotics, graphical animation and medical hand function assessment. There have been a number of hand-measurement devices constructed to date for measuring the position of the fingers; however, each such finger-measuring device has a common inadequacy, among various other shortcomings. The primary inadequacy of the devices being that they measure joint angles of the hand and then rely upon a mathematical model of the physical hand and "forward kinematic" mathematical calculations to produce an estimate of fingertip positions. Measuring finger joint angles explicitly is satisfactory when the goal of the device is to be used for measuring joint angles. However, in many of the aforementioned fields of study, the desired parameter to be measured is the position of the fingertip. When the position of the fingertip is desired, by measuring the finger joint angles and combining these angles with the mathematical model of the hand, errors in both the joint angle measurements and the model add to produce a cumulative error in fingertip position.
One common source of error is introduced by employing a simplified mathematical model of the hand, where each joint is approximated as a revolute joint with a fixed axis of rotation. More realistically, the instantaneous joint axis of a finger actually varies as a function of the joint angle. Additionally, measuring the joint angles of the finger often requires that a goniometer be affixed to phalanges comprising the links of the joint. Any unmeasured relative motion between these affixation points and the phalanges introduces error in the joint measurement. Hence, the number of such unmeasured affixation points is preferably kept to a minimum.
Devices which illustrate the above deficiencies are exemplified by the gloves described in U.S. Pat. Nos. 4,542,291, 4,937,444, 5,047,952, 5,280,265, 4,986,280, 5,086,785, 4,414,537, 5,184,009, 4,444,205, 5,316,017, 4,715,235.